Collaboration Involvement: Milagro
STACEE
VERITAS
Observations of the Unidentified TeV Gamma-Ray Source TeV J2032+4130 with the Whipple Observatory 10 m Telescope, A. Konopelko et al., Astrophys. J. 658, 1062 (2007).
Evidence for TeV Gamma-ray Emission from a Region of the Galactic Plane, R. Atkins et al., Phys. Rev. Lett. 95, 251103 (2005).
Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique, R. Atkins et al., Astrophys. J. 595, 803 (2003).
The High-Energy Gamma-Ray Fluence and Energy Spectrum of GRB 970417a from Observations with Milagrito, R. Atkins et al., Astrophys. J. 583, 824 (2003).
STACEE Observations of Markarian 421 during an Extended Gamma-Ray Outburst, L. M. Boone et al., Astrophys. J. Lett. 579, L5 (2002).
High Energy Gamma-Ray Observations of the Crab Nebula and Pulsar with the Solar Tower Atmospheric Cherenkov Effect Experiment, S. Oser et al., Astrophys. J. Lett. 547, 949 (2001).
Evidence for TeV Emission from GRB 970417a, R. Atkins et al., Astrophys. J. Lett. 533, L119 (2000).
Low energy photons from the 2.7 K cosmic microwave background or infrared starlight can collide with high-energy gamma rays to produce an electron-positron pair, effectively absorbing some of the gamma rays. For extragalactic sources, the amount of this absorption can probe the amount of intergalactic IR radiation. UCSC theorist Joel Primack and collaborators have been leaders in predicting how measurements of this absorption could distinguish between different cosmological models.
Satellites detect short bursts of low-energy gamma rays about once a day lasting from a fraction of a second to a few tens of seconds. Each gamma-ray burst is from a different location, and no one has yet been able to identify the burst sources with any particular known objects, nor has any burst has yet been detected above 30 GeV. Detection of bursts at TeV (10^12 eV) energies, or a definitive lack of emission, would help constrain models of burst production.
Milagro is a unique air-shower detector in the mountains west of Los Alamos, NM. It uses a 6 million gallon water reservoir equipped with 723 photomultipier tubes under a light-tight cover to detect showers of charged particles produced when gamma rays interact high in the atmosphere. Those relativistic particles from the shower which reach the ground produce Cherenkov light in the water which is detected by the phototubes. Milagro is sensitive to gamma-ray showers above about 100 GeV (10^11 eV), and views a large fraction of the overhead sky at any given moment. It is an ideal instrument to look for phenomena such as gamma-ray bursts in which the direction from which the next burst will come cannot be predicted.
STACEE uses the large array of mirrors at a solar power facility to detect atmospheric Cherenkov light produced by gamma-ray showers in the atmosphere. This technique is able to push the threshold for ground-based gamma-ray detection down below 100 GeV, while maintaining very good sensitivity.
VERITAS is a powerful new system of four 12-m imaging atmospheric Cherenkov Telescopes just being completed in winter 2007. It has substantially improved sensitivity compared to prior instruments such as STACEE.
Page revised March 2007